JP2007075882A - Rosin-based flux, and solder paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rosin-based flux capable of improving heating droop of a solder paste in a reflow furnace. <P>SOLUTION: The rosin-based flux contains rosin partial metallic salt and alkaline earth metal compound. The solder paste contains this rosin-based flux and solder powder. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rosin-based flux capable of improving the heating dripping of solder paste in a reflow furnace, and a solder paste with improved heating dripping.

As electronic devices become more functional and smaller and lighter, miniaturization of parts and higher accuracy of patterns are progressing more than before, and surface-mount substrates are now micro-solder bonding called micro soldering. Manufactured with technology.

  In micro soldering, printing is usually performed after solder paste, which is a mixture of paste-like rosin flux and powder-like solder alloy, is placed on a minute terminal electrode on a substrate by screen printing. The substrate is soldered by passing it through a heating furnace called a reflow furnace. In the reflow furnace, the main heating (usually about 200 to 360 ° C.) for melting the solder alloy after the substrate preheating (usually about 150 to 160 ° C.) is usually performed for soldering. I do.

  Here, the rosin flux refers to a viscous composition made from rosins, thixotropic agents, solvents, activators and the like. The rosin flux maintains the shape of the solder paste printed on the terminal electrode during preheating, and also removes the oxide film present on the surface of the solder alloy and terminal electrode during the main heating to promote wetting of both. There are effects such as. The thixotropic agent is mainly responsible for maintaining the shape, and the activator is mainly responsible for removing the oxide film, but the rosins impart an appropriate viscosity to the flux and are inactive at normal temperatures before and after soldering. There is the convenience that the effect can be expressed simultaneously.

By the way, during the preheating of the reflow furnace, the solder paste placed on the terminal electrode is heated and drowned (the solder paste loses thixotropic property and becomes excessively softened or liquefied, and the terminal is put together with unmelted solder alloy powder. (Refers to a phenomenon of flowing out around the electrode). If the degree of heating is large, solder balls are formed in the vicinity of the terminal electrodes and solder bridges are formed between the terminal electrodes, and the insulation reliability of the surface mount substrate is significantly impaired.

Thus, conventionally, a method using a thixotropic agent that gives excellent thixotropic properties (see Patent Document 1) and a method using a specific high-boiling solvent (see Patent Document 2) have been proposed. Although a good effect can be obtained to some extent, other problems such as a flux residue that is difficult to clean and a melting dripping at the time of main heating without evaporation of the solvent occur.

Japanese Patent Laid-Open No. 10-328882 Japanese Patent Laid-Open No. 10-193176

The present invention provides a novel rosin-based flux capable of improving the solder paste of a solder paste in a reflow furnace from the viewpoint of rosins having high convenience as a flux material without using a special thixotropic agent or solvent. The main purpose.

Considering that the main factor of the heating dripping is a decrease in the thixotropic property of the solder paste during preheating, the present inventor has earnestly devised a novel rosin-based material capable of suppressing such a decrease in thixotropic property. Repeated examination.

As a result, it has been found that the above-mentioned problems can be solved by using an alkaline earth metal compound in combination with the rosin partial metal salt.

That is, the present invention relates to a rosin-based flux (hereinafter abbreviated as a flux) containing a rosin partial metal salt (A) and an alkaline earth metal compound (B); and a solder paste containing the flux and solder powder.

According to the flux of the present invention, heating dripping of the reflow furnace solder paste can be improved. Therefore, if a solder paste using the flux is used, the frequency of occurrence of the solder balls and solder bridges can be remarkably reduced.

In the flux of the present invention, the use of a mixture of the rosin partial metal salt (A) and the alkaline earth metal compound (B) can improve the heating. The reason for this is not clear, but the reaction between the two in the flux will probably generate a resin acid-alkaline earth metal salt compound, and the compound will form a stacking structure. This is thought to be caused by The stacking structure is released during the main heat, and the regenerated resin acid is considered to contribute to the action of cleaning the solder alloy surface. On the other hand, when only the rosin partial metal salt (A) is used, an effect of suppressing heating dripping is hardly obtained, and a white residue that is difficult to clean after soldering is rather produced.

The rosin partial metal salt (A) is a reaction product of various known rosins and metal compounds. The rosin partial metal salt (A) may contain both a resin acid that forms the metal salt and a resin acid that does not, but preferably achieves the effect of suppressing the heating dripping. For the purpose, it is preferred that the resin acid forming the metal salt is contained in an amount of 70 mol% or more, preferably 80 to 95 mol%.

The metal compound is not particularly limited as long as it can form a salt with the resin acid. Specifically, hydroxides, oxides, chlorides, nitrates, acetates, sulfates and carbonates of alkali metals such as lithium, sodium and potassium and alkaline earth metals such as magnesium, calcium, strontium and barium These can be exemplified, and these can be used in combination of two or more. The metal compound is preferably an alkaline earth metal, particularly magnesium and / or calcium in consideration of the effect of suppressing heating dripping.

Examples of the rosins include natural rosins such as gum rosin, wood rosin and tall oil rosin; various processed products of the natural rosins (rosin, disproportionated rosin, dehydrogenated rosin, etc.); various modified products of the natural rosins (Polymerized rosin, α, β-ethylenically unsaturated carboxylic acid-modified rosin (acrylated rosin), polyhydric alcohol ester, formylated rosin); hydrides of these purified products and corresponding ones can be exemplified. Can be used alone or in combination of two or more. As the rosin, the hydrogenated rosin is preferable because the heat resistance of the flux can be improved. In addition, the resin acid is selected from the group consisting of abietic acid, levopimaric acid, neoabietic acid, parastrinic acid, pimaric acid, isopimaric acid, sandaracopimalic acid, dehydroabietic acid, dihydroabietic acid and tetrahydroabietic acid. And one type.

  The production method of the rosin partial metal salt (A) is not particularly limited, and various known methods can be employed. Specifically, for example, a method described in JP-A-9-71729 may be employed.

Specific examples of the alkaline earth metal compound (B) include at least one hydroxide, oxide, chloride, nitrate, acetate, sulfate, and carbonate selected from the above alkaline earth metals. . More specifically, for example, magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide and the like can be exemplified, and these can be used in combination of two or more. Among these, calcium hydroxide is preferable because the desired effect of the present invention can be easily obtained.

The rosin partial metal salt (A) and the alkaline earth metal compound (B) may be used separately or may be used in combination. The latter is preferable in consideration of the effect of suppressing heating drool.

  The content of the rosin partial metal salt (A) and the alkaline earth metal compound (B) in the flux can be appropriately determined by paying attention to the effect of suppressing the heating dripping, but usually the total of both is 0.5 to It is about 10.0% by weight, preferably 1.5 to 5.0% by weight. Note that even if the upper limit is exceeded, the effect of suppressing heating dripping is not impaired, but another problem such as difficulty in melting the solder powders tends to occur.

The weight ratio of the rosin partial metal salt (A) and the alkaline earth metal compound (B) used in the flux can be appropriately determined by paying attention to the effect of suppressing the heating dripping. It is about 1-1: 3.

  The flux of the present invention contains a rosin, a thixotropic agent, a solvent, an activator and the like in addition to the rosin partial metal salt (A) and the alkaline earth metal compound (B).

As the rosins, the same rosins as described above can be used. In particular, since it has excellent heat resistance and contributes to suppression of the heating dripping, the hydrogenated rosin, disproportionated rosin, (hydrogenated) polymerized rosin, (hydrogenated) acrylated rosin, (hydrogenated) polyhydric alcohol At least one selected from the group consisting of esters, particularly hydrogenated rosin and / or (hydrogenated) acrylated rosin is preferred. The content of the rosin in the flux is usually about 10.0 to 75.0% by weight, preferably 20.0 to 60.0% by weight.

Examples of the thixotropic agent include castor oil, hydrogenated castor oil, beeswax, carnauba wax, stearamide, hydroxystearic acid ethylenebisamide, and the like, and two or more of these may be used in combination. The content of the thixotropic agent in the flux is usually about 0.1 to 10.0% by weight, preferably about 0.1 to 5.0% by weight.

As the solvent, any solvent that can be used for a rosin flux can be used without any particular limitation. Specifically, for example, ethylene glycol monohexyl ether, diethylene glycol monobutyl ether, hexyl glycol, hexyl carbitol, octanediol, ethylhexyl glycol, benzyl alcohol, 1,3-butanediol, 1,4-butanediol 2- (2- n-butoxyethoxy) alcohols such as ethanol and terpineol; esters such as butyl benzoate, diethyl adipate and 2- (2-n-butoxyethoxy) ethyl acetate; hydrocarbons such as dodecane and tetradecene; N-methyl Examples include pyrrolidones such as -2-pyrrolidone, and two or more of these may be used in combination. The content of the solvent in the flux is usually about 24.3 to 85.0% by weight, preferably about 30.0 to 75.0% by weight.

  The activator can be used without particular limitation as long as it can be used for flux. Specifically, for example, succinic acid, benzoic acid, adipic acid, abietic acid, glutaric acid, palmitic acid, stearic acid, formic acid or azelaic acid, ethylamine hydrochloride, methylamine hydrochloride, ethylamine hydrobromide, diethylamine odor Hydrochloride, methylamine hydrobromide, propenediol hydrochloride, allylamine hydrochloride, 3-amino-1-propene hydrochloride, N- (3-aminopropyl) methacrylamide hydrochloride, O-anisidine hydrochloride , N-butylamine hydrochloride or P-aminophenol hydrochloride, quaternary ammonium, lauryltrimethylammonium chloride, alkylbenzyldimethylammonium chloride and the like, and two or more of these may be used in combination. The content of the activator in the flux is usually about 0.1 to 10.0% by weight, preferably about 0.1 to 5.0% by weight.

  In the present invention, various known additives may be used. Specifically, for example, tributylamine, tetrabutylammonium bromide, 2,6-di-t-butyl-p-cresol, para-tert-amylphenol, 2,2′-methylenebis (4-methyl-6-tert- Butylphenol), trans-2,3-dibromo-2-butene-1,4-diol, antioxidants such as 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol 3,5-dimethyl-1-hexyn-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,4,7,9-tetramethyl-5-decyne-4,7- Anti-skinning agents such as diol and 3,6-dimethyl-4-octyne-3,6-diol can be used. The content of the additive in the flux is usually about 0 to 10.0% by weight, preferably 0 to 5.0% by weight.

In the present invention, various known synthetic resins may be used in combination. Specifically, for example, epoxy resin, acrylic resin, polyimide resin, polyamide resin (nylon resin), polyester resin, polyacrylonitrile resin, vinyl chloride resin, vinyl acetate resin, polyolefin resin, fluorine-based resin, ABS resin, isoprene Elastomers such as rubber, styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber or nylon rubber, nylon elastomer, polyester elastomer and the like can be exemplified, and these can be used in combination of two or more. The content of the synthetic resin in the flux is usually about 0 to 20% by weight, preferably 0 to 10% by weight.

The flux of the present invention can be obtained, for example, by kneading the above-mentioned raw materials using a planetary mill or the like. The kneading conditions are not particularly limited, and are usually room temperature and normal pressure.

The solder paste of the present invention is obtained by kneading solder powder into the flux by various known means so that the weight ratio of the former to the latter is usually about 10:90.

  As solder powder, Sn solder powder, Sn-Ag solder powder, Sn-Ag-Cu solder powder, Sn-Ag-Bi solder powder, Sn-Ag-Cu-Bi solder powder, Sn-Ag-Cu-In solder powder , Lead-free solder powder such as Sn-Ag-Cu-S solder powder, Sn-Ag-Cu-Ni-Ge solder powder; Sn-Pb solder powder, Sn-Pb-Ag solder powder, Sn-Pb-Bi Examples thereof include lead eutectic solder powders such as Pb-based solder powder, In-Pb solder powder, and Pb-Ag solder powder. In view of environmental problems, lead-free solder powder is preferred.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely through an Example, this invention is not limited to these Examples.

(Flux preparation)
The raw materials shown in Table 1 were mixed with a planetary mill to prepare a rosin solder flux.

(Preparation of solder paste)
Sn-Ag-Cu-based solder metal powder (Sn96.5 wt%, Ag3 wt%, Cu0.5 wt%; trade name "Sn96.5 / Ag3 / Cu0.5") was added to 10 parts of the flux (solid content weight). 90 parts of Mitsui Kinzoku Mining Co., Ltd.) was added and kneaded in a planetary mill for 1 hour to prepare a solder paste.

Examples 1-3, Comparative Example 1
(Evaluation of who heated)
Screen printing was performed on the solder paste copper substrate in a rectangular shape of 1.0 mm × 3.0 mm × 70.0 μm at intervals of 0.4 mm (metal squeegee speed: 20.0 mm / second, plate separation speed: 0.1 mm / second) ). Subsequently, it heated for 90 second in the nitrogen reflow furnace (preheating: 150-160 degreeC), the change of the shape of this solder paste was observed visually, and what was heated with reference to the following references | standards was evaluated.

○: The shape of the solder paste printed in a rectangular shape is maintained.
(Triangle | delta): The solder paste printed in the rectangular shape is dripping at the periphery.
X: The solder paste printed in a rectangular shape is slanted at the periphery and is in a contact state.

Claims (9)

A rosin flux containing a rosin partial metal salt (A) and an alkaline earth metal compound (B). The rosin flux according to claim 1, wherein the metal content of the rosin partial metal salt (A) is an alkaline earth metal. The rosin flux according to claim 2, wherein the alkaline earth metal is magnesium and / or calcium. The rosin flux according to any one of claims 1 to 3, wherein the alkaline earth metal compound (B) is calcium hydroxide. The rosin-based flux according to any one of claims 1 to 4, wherein the total content of the rosin partial metal salt (A) and the alkaline earth metal compound (B) is 0.5 to 10% by weight. The rosin-based flux according to any one of claims 1 to 5, wherein a weight ratio of the rosin partial metal salt (A) and the alkaline earth metal compound (B) used is 3: 1 to 1: 3 in the former to the latter. The rosin flux for solder according to any one of claims 1 to 6, further comprising rosins, a thixotropic agent, a solvent, and an activator. A solder paste comprising the rosin flux according to any one of claims 1 to 7 and solder powder. The solder paste according to claim 8, wherein the solder powder is a lead-free solder powder.